Methods of protecting furnace electrodes with cooling liquid that contains an additive

ABSTRACT

A method for forming a protective antioxidative barrier on the furnace electrodes using a chemically altered cooling liquid containing an antioxidant additive. This method can be applied to electrodes used in electric arc furnaces and ladle metallurgy furnaces. The method can involve spraying the cooling liquid onto the electrode, thereby forming the protective antioxidative barrier and reducing the oxidation of the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims the benefit of U.S. ProvisionalApplication No. 62/779,457, filed Dec. 13, 2018, and U.S. ProvisionalApplication No. 62/745,697, filed Oct. 15, 2018.

FIELD OF DISCLOSURE

This disclosure relates to the implementation of a novel process wherebythe electrode cooling water in an electric arc furnace (EAF) or ladlemetallurgy furnace (LMF), or any variation of a furnace that uses watercooled electrodes in the steel making process is chemically modified.The modification provides reduced sidewall oxidation of the electrodethrough the formation of a protective barrier on exterior surfaces ofthe furnace electrodes, resulting in extended electrode life.

BACKGROUND

EAF steel producers use electrical energy to melt raw materials toproduce 1 ton to 420 metric tons of steel in vessels. Electrical energycan be delivered to the furnace as alternating current (AC) or directcurrent (DC). The electrical power delivered to the raw materials can beas high as 200 MWh in the case of the largest EAF vessels. This powersupply creates an electrical arc that creates the necessary heat toraise the batch of steel to temperatures as high as 1800° C. and toallow for further refinement and processing in the LMF and subsequentcasting and forming operations.

The electrical power is delivered to the steel through graphiteelectrodes. Graphite is the material of choice for electrodes due to thefollowing characteristics: low coefficient of thermal expansion (CTE),high tensile strength, high specific resistance, electrical resistancethat is relatively independent of temperature, and nobility (cathodic toother materials).

Electrodes are consumables utilized in the electrical steel makingprocess and account for a substantial cost for the steel maker. Theenvironment in the electric arc furnace is violent and harsh, and causesconsumption of electrodes in a range of approximately 1 kg/metric ton ofsteel produced to 2.5 kg/metric ton. Causes of consumption include:electrical arc at the electrode tip where localized temperature isapproximately 3000° C.; electrode breakage due to movement of rawmaterials; thermal shock and subsequent loss of electrode tip; andoxidation of the electrode surfaces along the column due to the harshfurnace environment. Oxidation of the electrode creates the conicalshape of electrodes that are in use and can account for nearly 50% ofthe electrode consumption.

For decades, steel producers and furnace electrode producers haveattempted to reduce the oxidation rate of the graphite and carbonelectrodes through many different means. One example is to useelectrodes that have surfaces coated with layers formed from graphite,metal, aluminum alloys, and pure aluminum. However, these coatings areonly applied once (e.g., only during the manufacturing of theelectrodes), and the coatings are susceptible to chemical and physicaldamage that renders them ineffective. Thus, these type of coatings canhave short useful life spans.

Changes in the electrode manufacturing process, in electrode couplingtechnology, in the recipe for the graphite electrodes, and inoperational procedures like foamy slag have substantially reducedelectrode consumption since 1985 when electrode consumption was between5 to 6 kg/metric ton of steel, to 1 to 2.5 kg/metric ton of steel in2018. While this has been an impressive reduction, market forces haveheightened sensitivity to the consumption rate. Even incrementaldecreases in consumption rate have a substantial impact to the steelmaker.

The oxidation of the electrode is a chemical reaction. The rate ofoxidation of the electrode increases with increasing temperaturesbecause the reactant molecules have more kinetic energy at highertemperatures. The reaction rate (i.e., oxidation rate) is governed bythe Arrhenius equation which in almost all cases shows an exponentialincrease in the rate of reaction as a function of temperature.

$k = \frac{- {Ea}}{k_{B}T}$

Where: k=the rate constant

k_(B)=Boltzmann constant

T=absolute temperature

A=a constant for each chemical reaction

E_(a)=the activation energy

R=the universal gas constant

Therefore, many designs have been developed to cool the bulk of theelectrode (i.e., lower the temperature of the electrode), but have beenabandoned due to safety concerns. Applying cooling water to theelectrode below the molten steel bath creates a very dangerous conditionin the case of an electrode break or the failure of the cooling waterchannel. The release of cooling water below the steel bath creates anexplosion due to the rapid expansion as the water changes phase fromwater to steam with an approximate volumetric expansion of 1,100 times.Electrodes used in commercial steel making are currently composedexclusively of graphite and do not contain cooling water channels.

To further reduce oxidation of the electrode, spray cooling wasintroduced to the industry and specific designs to cool the electrodeusing circular spray headers with multiple vertical spray headerslocated at multiple locations around the circumference of the electrode.

Investigation of water application has been employed to enhance safetyas well as mitigate oxidation of the electrode. Enhancements, such asproviding air to atomize the water as it is discharged from the spraynozzle, have been evaluated. Electrode cooling water flow, in somefacilities, varies depending upon the furnace conditions, providing anadditional level of safety.

SUMMARY

In contrast to known techniques, and as disclosed herein, the process ofadding an additive to the spray water system surprisingly can form aneffective protective barrier on a surface of the electrode to reduceoxidative consumption of the electrode. In some aspects, this approachcan provide beneficial protection over the electrode length, where thecoating can exist as a precipitate coating on at least a portion of theexterior surface of the electrode that is above the furnace and asmolten coating on at least a portion of the exterior surface of theelectrode that is below the furnace. In other aspects, the presence ofthe protective barrier coating can be maintained by constantly sprayingthe cooling liquid onto the surface of the electrode so as to providecontinuous protection against sidewall oxidation, e.g., during a steelmaking processes. In some aspects, this approach can simplify thetransportation, packaging, and handling processes.

Thus, one objective of the present disclosure is to provide a method forchemically modifying the electrode cooling water to reduce the side walloxidation of the furnace electrode, resulting in increased life of theelectrode during the steel making process.

An aspect of the disclosure is a method for forming a protective barrieron a furnace electrode, the method including: (i) providing electrodecooling water, (ii) mixing an antioxidant additive with the electrodecooling water to form a cooling liquid, (iii) spraying at least asurface of the furnace electrode disposed adjacent a furnace with thecooling liquid, thereby cooling the furnace electrode, and (iv) forminga protective antioxidative barrier on the furnace electrode, theprotective antioxidative barrier includes the antioxidant additive whichhas been deposited and/or precipitated on the furnace electrode from thecooling liquid.

Another aspect of the disclosure is a method for forming a protectivecoating on a furnace electrode that has a surface heated to atemperature of at least 700° C., the method including: (i) providing acooling liquid that includes water and an antioxidant additive; and (ii)applying the cooling liquid to the surface of the furnace electrode sothat the water evaporates and the antioxidant additive precipitates andforms the protective coating on the furnace electrode.

Another aspect of the disclosure is a method for cooling a furnaceelectrode, the method including: (i) dissolving an antioxidant additivein water to form a cooling liquid in which the antioxidant additive ispresent in an amount of from 100 mg/L to 5,000 mg/L; and (ii) applyingthe cooling liquid to a surface of the furnace electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a spray cooling system for asingle electrode in a direct current furnace.

FIG. 2 is a schematic diagram illustrating a spray cooling system withfeedback and control of individual electrode cooling banks for each ofthe three electrodes in an alternating current furnace.

FIG. 3 is a schematic diagram illustrating a spray cooling system withfeedback and control of individual electrode cooling banks and achemical metering skid for the electrodes in an alternating currentfurnace.

FIG. 4 is a graph showing the relative electrode consumption by weightof produced steel.

FIG. 5 is a graph showing the relative electrode consumption by weightof produced steel.

DETAILED DESCRIPTION OF EMBODIMENTS

The disclosed cooling methods may be used to cool any high-temperaturefurnace electrodes that are conventionally cooled using water. Forexample, the disclosed cooling methods may be used to cool graphiteelectrodes in furnaces and/or steel making processes such as electricarc furnace, induction furnace, vacuum induction melting, argon oxygendecarburization, ladle furnace, vacuum oxygen degassing, vacuumdegassing, vacuum arc remelting, and electro slag remelting. When thefurnace electrode is in use, a surface of the furnace electrode can havea temperature of at least 700° C., at least 1000° C., at least 1200° C.,at least 1800° C., or at least 3000° C.

As used herein, the term “antioxidant additive” refers to a compoundthat can form a protective antioxidative coating on the surface of theelectrodes, and includes any precipitating-type chemistry or similartype chemistry that increases the total dissolved solids of the spraywater, in which the additive in the cooling liquid precipitates ordeposits on a surface of the electrode to form a protective coating. Asused herein, the singular term “additive” can refer to either oneadditive or combinations of two or more additives. Mixing an antioxidantadditive with water to form a chemically modified cooling liquid canallow the water to transport the antioxidant additive to the surface ofthe electrode where the heat from the electrode causes the water to boiloff and the additive to precipitate and deposit on the electrode surfaceto form a protective barrier on the electrode surface. Thus, under thisapproach, an additive is added to a cooling liquid so that the additiveintentionally precipitates out of the solution in a beneficial way,which is contrary to conventional practices where precipitatingcomponents in industrial cooling systems are considered to beproblematic.

In some aspects, the protective barrier that is formed can exist as atwo-phase coating on an exterior surface of the electrode. Above thefurnace, the coating can exist as a layer of the precipitates/deposits(typically, as chalky white layer). This layer is believed to provideoxidative protection by shielding the graphite surface of the electrodefrom atmospheric oxygen and thus can reduce the rate of side walloxidation. The precipitates/deposits layer can enter the furnace whennewer portions of the electrode are moved into the furnace as theelectrode is consumed during use. Once the precipitates/deposits layeris near or inside the furnace, the precipitates/deposits can melt toprovide a molten coating on an exterior surface of the electrode that iswithin the furnace. This molten coating is also believed to shield thesurface of the electrode from oxygen to reduce side wall oxidation. Itis believed that the molten coating runs down substantially the entirelength of the electrode (e.g., at least 90%) to the electrode tip toprovide oxidative protection along the surface of the electrode that iswithin the furnace. In some aspects, this technique can providecontinuous oxidative protection during electrode use over substantiallythe entire electrode length since the precipitates/deposits layer isbeing formed on the electrode above the furnace as the spray coolingwater is applied, and the molten coating is continuously formed on aportion of the electrode below the furnace as the electrode is movedinto the furnace.

The melting point of the at least one of the antioxidant additives inthe cooling water, including one of the primary additives that areadded, can be higher than the temperature at which rapid oxidation ofthe electrode material (e.g., graphite) occurs (e.g., about 700° C.).For example, the melting point of the at least one antioxidant additivecan be at least 710° C., at least 900° C., at least 1,000° C., at least1200° C., or at least 1,500° C., at least 2,000° C., at least 2400° C.,and up to 3,000° C., or up to 2,800° C. This at least one antioxidantadditive can also be soluble in water. For example, a solubility of theat least one antioxidant additive can be at least 10 mg/L, at least 100mg/L, at least 500 mg/L, or at least 1 g/L. In some embodiments, theantioxidant additive can be insoluble in water.

The cooling liquid can be predominantly water, e.g., more than 95 wt %,more than 99 wt %, or more than 99.5 wt %. In some embodiments, thecooling liquid can contain 10-70 wt %, 15-60 wt %, or 20-50 wt % water,based on a total weight of the cooling liquid. In some embodiments, thewater can be recycled process water or municipal water.

The concentration of the antioxidant additive in the cooling liquid canbe present in amounts sufficient to form a protective barrier on theelectrode. Depending on the diameter of the furnace electrode, a totalamount of the antioxidant additive may be in the range of from 10 mg/lto 1,000 mg/l, from 25 mg/l to 850 mg/l, from 50 mg/l to 800 mg/l, from100 mg/l to 600 mg/l, or from 200 mg/l to 650 mg/l. In some embodiments,the amount of antioxidant additive ranges from 30-90 wt %, 40-85 wt %,or 50-80 wt %, based on a total weight of the cooling liquid. In someembodiments, at least 95 wt % of the antioxidant additive that is addedto the cooling liquid goes into solution, i.e., at the stage where it ismixed with the cooling liquid, and in some embodiments all of theantioxidant additive that is added to the cooling liquid goes intosolution.

The amount of additive that is added to the cooling water can be anamount that is sufficient to provide a protective barrier on the furnaceelectrode. Generally, more dissolved solids in the cooling liquid willprovide more precipitated solids that are deposited on the furnaceelectrode after the cooling liquid is sprayed onto the electrode.However, in some embodiments, the amount and type of additive should notexceed an amount that would cause substantial precipitation of theadditive in the spray nozzles or the conduits thereof. In this regard,the spray nozzles and the associated conduits also operate at extremelyhigh temperatures, and the amount and type of antioxidant additive canbe selected (e.g., based on the solubility of the additive in thecooling liquid) so that the cooling liquid can be sprayed in the desiredquantities to form a robust protective barrier on the electrode withoutscaling or clogging in the spray nozzles or with minimalscaling/clogging. To further prevent scaling/clogging, the additive caninclude a scale inhibitor or dispersant, and examples of these areprovided below.

In some aspects, a sufficient amount of antioxidant additive is added tothe cooling liquid to form a protective barrier coating on a surface ofthe electrode when the cooling liquid is applied to the electrode. Abovethe furnace, the protective barrier coating can have a thickness rangingfrom 0.005 to 1 mm, 0.01 to 0.7 mm, or from 0.05 to 0.3 mm. In someembodiments, the thickness of the protective barrier is not more than 5mm, or 2 mm. The cooling water can be sprayed so that the protectivebarrier coating has a substantially uniform structure on an exteriorsurface of the electrode that is above the furnace, i.e., so that thereare no patches where the electrode is exposed and so the coatingthickness is substantially constant across the surface (e.g., deviatingby no more than 20% from an average thickness). Above the furnace, theprotective barrier coating typically has a white, chalky or frostedappearance. This coating can be formed to have sufficient structuralintegrity and cohesiveness to withstand the harsh environment duringelectrode use, including high temperatures and mechanical vibrations. Inthis regard, the coating can form a tenacious protective barrier thatdoes not flake or otherwise come off of the electrode surface duringuse. As described above, it is believed that at least some of theprecipitated/deposited antioxidant additive becomes molten inside thefurnace, which forms a molten coating that flows downward along theexterior surface of the electrode toward the tip of the electrode.

The method provided herein can use any suitable antioxidant additive andis not inherently limited to any specific chemistries. In this regard,it is believed that the protective barrier coating can be provided bysufficient dissolved solids in the cooling water. Exemplary antioxidantadditives suitable for use in the present method include fluorides(e.g., alkali metal fluorides; alkaline earth metal fluorides, such ascalcium fluoride and magnesium fluoride; transition metal fluorides;post-transition metal fluorides; ammonium fluorides; and sodium aluminumfluoride), chlorides (e.g., alkali metal chlorides; alkaline earth metalchlorides, such as calcium chloride and magnesium fluoride; transitionmetal chlorides; post-transition metal chlorides; and ammoniumchlorides), bromides (e.g., alkali metal bromides; alkaline earth metalbromides, such as calcium bromide and magnesium bromide; transitionmetal bromides; post-transition metal bromides; and ammonium bromides),nitrates (e.g., alkali metal nitrates; alkaline earth metal nitrates,such as calcium nitrate and magnesium nitrate; transition metalnitrates; post-transition metal nitrates; and ammonium nitrates),sulfates (e.g., alkali metal sulfates; alkaline earth metal sulfates,such as calcium sulfate and magnesium sulfate; transition metalsulfates; post-transition metal sulfates; and ammonium sulfates),silicates (e.g., alkali metal silicates), phosphates or orthophosphates(e.g., alkali metal salts or alkaline earth metal salts, such as calciumor magnesium salts, or transition metal salts or post-transition metalsalts or ammonium salts of orthophosphoric acid, aluminumorthophosphate), phosphate derivatives or polyphosphates (e.g., alkalimetal salts or alkaline earth metal salts, such as calcium or magnesiumsalts, or transition metal salts or post-transition metal salts orammonium salts of pyrophosphoric acid, tripolyphosphoric acid,tetrapolyphosphoric acid, and trimetaphosphoric acid, and alkali metalhexametaphosphate), alkali metal salts or alkaline earth metal salts ofboric oxide, metaboric acid, or boric acid (e.g., sodium borate), sodiumborofluoride, and combinations thereof. In some embodiments, theantioxidant additive is an alkali metal hexametaphosphate (e.g., sodiumhexametaphosphate), an alkaline earth metal hexametaphosphate, atransition metal hexametaphosphate, ammonium hexametaphosphate, analkali metal salt of pyrophosphoric acid (e.g., tetrasodiumpyrophosphate), an alkaline earth metal salt of pyrophosphoric acid(e.g., a calcium salt of pyrophosphoric acid, a magnesium salt ofpyrophosphoric acid), a transition metal salt of pyrophosphoric acid, anammonium salt of pyrophosphoric acid, or combinations thereof.

As used herein, the term “alkali metal” refers to lithium, sodium,potassium, rubidium, and cesium. The term “alkaline earth metal” refersto beryllium, magnesium, calcium, strontium, and barium. The term“transition metal” refers to scandium, titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium,molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum,tungsten, rhenium, osmium, iridium, platinum, and gold. The term“post-transition metal” refers to aluminum, indium, gallium, tin,bismuth, lead, thallium, zinc, cadmium, and mercury.

The term “ammonium” refers to a cation formed from an amine and ahydrogen ion. Exemplary amines include ammonia, a primary aminerepresented by formula NH₂R, a secondary amine represented by NHR₂, anda tertiary amine represented by formula NR₃, where each R isindependently an optionally substituted alkyl, an optionally substitutedaryl, and an optionally substituted arylalkyl. The term “alkyl”, as usedherein, refers to a straight, branched, or cyclic hydrocarbon fragment.Non-limiting examples of such hydrocarbon fragments include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl,neopentyl, hexyl, isohexyl, 3-methylpentyl, 2,2-dimethylbutyl, and2,3-dimethylbutyl. As used herein, the term “cyclic hydrocarbon” refersto a cyclized alkyl group. Exemplary cyclic hydrocarbon (i.e.cycloalkyl) groups include, but are not limited to, cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl, norbornyl, and adamantyl. Branchedcycloalkyl groups, such as exemplary 1-methylcyclopropyl and2-methycyclopropyl groups, are included in the definition of cycloalkylas used in the present disclosure. The term “aryl,” as used herein, andunless otherwise specified, refers to a substituent that is derived froman aromatic hydrocarbon (arene) that has had a hydrogen atom removedfrom a ring carbon atom. Aryl includes phenyl, biphenyl, naphthyl,anthracenyl, and the like. The term “arylalkyl” as used in thisdisclosure refers to a straight or branched chain C₁ to C₈ alkyl moietythat is substituted by an aryl group or a substituted aryl group having6 to 12 carbon atoms. “Arylalkyl” includes benzyl, 2-phenethyl,2-methylbenzyl, 3-methylbenzyl, 4-methylbenzyl, 2,4-dimethylbenzyl,2-(4-ethylphenyl)ethyl, 3-(3-propylphenyl)propyl.

In some embodiments, the cooling liquid contains a mixture of an alkalimetal hexametaphosphate and an alkali metal salt of pyrophosphoric acid.A ratio of the weight of alkali metal hexametaphosphate to the weight ofthe alkali metal salt of pyrophosphoric present in the cooling liquid isin a range of from 1:100 to 100:1, from 1:50 to 50:1, or from 1:10 to10:1.

In some embodiments, a mixture of a salt of hexametaphosphate and a saltof pyrophosphoric acid is added to the cooling water. The cations ofthese salts can be exchanged with the alkali metal cations or alkalineearth metal cations (e.g., calcium) initially present in the coolingwater to form in situ alkali metal salts (or alkaline earth metal salts)of hexametaphosphate and pyrophosphoric acid. In some embodiments, whenan alkali metal hexametaphosphate (e.g., sodium hexametaphosphate) isadded to the cooling water, the alkali metal cation can be exchangedwith the alkaline earth metal cations (e.g., calcium) initially presentin the cooling water to form in situ alkaline earth metal phosphate(e.g., calcium phosphate), alkaline earth metal phosphonate, and/oralkaline earth metal trimetaphosphate, which in turn are sprayed ontothe furnace electrode to form the protective barrier. In someembodiments, alkaline earth metal cations (e.g., in the form of calcium,such as calcium chloride) are deliberately added to the cooling water tofacilitate the formation of the protective barrier.

The specific additive(s) can be selected depending on the initial waterchemistry of the spray water that is used to cool the electrode and thefinal water chemistry of the spray water (i.e., after the additive isadded). This selection can depend on several factors that are specificto the particular furnace, including the ability to form a moltencoating in the furnace while the electrode is in use. In someembodiments, specific compounds may be considered to be particularlyuseful additives for forming the protective coating, such as one or moreof phosphates, phosphonates, calcium salts, magnesium salts, molybdates,borates, and silicates. In some embodiments, including Examples 2-4below, the cooling water can contain (i) one or more additive selectedfrom phosphates, phosphonates, calcium salts, magnesium salts,molybdates, boron salts, and silicates, and (ii) one or more additiveselected from a scale inhibitor and a dispersant.

In some embodiments, the additive can be selected so that the coolingliquid can have a hardness of at least 0.5 mmol/L, at least 1.0 mmol/L,at least 1.5 mmol/L, or at least 3 mmol/L. In some embodiments, thehardness is not more than 4 mmol/L, not more than 2 mmol/L, or not morethan 1.2 mmol/L. As used herein, the term “hardness” refers to the sumof the molar concentrations of calcium and magnesium ions in the coolingliquid. It is believed that using a cooling liquid having a higherhardness can improve the formation of the protective barrier by, forexample, increasing the speed of formation of the protective barrier.

The additive can also include a scale inhibitor to prevent scaling inthe nozzle or conduits, such as scale inhibitors and dispersantsselected from the group consisting one or more of unsaturated carboxylicacid polymers such as polyacrylic acid, homo or co-polymaleic acid(synthesized from solvent and aqueous routes);acrylate/2-acrylamido-2-methylpropane sulfonic acid (APMS) copolymers,acrylate/acrylamide copolymers, acrylate homopolymers, terpolymers ofcarboxylate/sulfonate/maleate, terpolymers of acrylic acid/AMPS;phosphonates and phosphinates such as2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), amino tris methylene phosphonicacid (ATMP), 2-hydroxyphosphonocarboxylic acid (HPA), and combinationsthereof.

Industrial application of this method indicates that an additional 2 to40 percent, 2 to 30 percent, 5 to 20 percent, or 3 to 15 percentelectrode consumption is avoided through the implementation of thismethod. For example, the protective coating can reduce oxidativeelectrode consumption by 2 to 30 percent as compared to a like method inwhich only water cools the furnace electrode. As would be appreciated inthe art, a reduction in oxidative electrode consumption of even 2percent is considered to be significant and can provide for substantialsavings. Electrode consumption is typically determined over a period oftime. For example, in one embodiment, the electrode consumption iscalculated as the consumption over one week period. In otherembodiments, the consumption may be calculated over a two week period.In still other embodiments, the electrode consumption is calculated overa one month period. In still further embodiments, the consumption iscalculated for periods longer than about 3 days. In some embodiments,the consumption is calculated weekly or monthly. Electrode consumptioncan be determined by methods known to one skilled in the art, forexample, by measuring the value of the eddy current in the electrode,which can be correlated to the consumption rate. See U.S. Pat. No.4,048,556 to Roach et al., which is incorporated herein by reference inits entirety. In some embodiments, actual electrode consumption can bemeasured in the process of replacing the furnace electrodes per ton ofproduced steel. For example, the number of heats of a known mass ofsteel produced by the furnace (e.g., the EAF or LMF) per electrode canbe measured. As an another example, electrode consumption can bemeasured by removing the electrode, weighing the electrode, andrepeating this process for other electrodes that are used within aspecified time period.

FIG. 1 illustrates an example of a spray cooling arrangement for adirect current furnace. The electrode holder 2 holds the graphiteelectrode 1 which extends into the furnace through the top of thefurnace 6. The size of the graphite electrode 1 can typically vary from75 mm to 700 mm in diameter, although electrodes of up to 800 mm areavailable. The antioxidant additive and water can be pre-mixed offlineto form a cooling liquid which is supplied to the flow path 13 via thepump 8 (e.g., a booster pump).

The spray cooling system (i.e., the cooling bank) has a circular ringdistribution header 3 and a vertical spray distribution header 4. Thevertical spray distribution header 4 includes a plurality of nozzles 5 afrom which the cooling liquid 5 is sprayed onto the outer circumferenceof the electrode 1. In this manner, the cooling of the electrode occursfrom the electrode holder 2 to the top of the furnace 6. At the point ofimpingement, or where the water meets the electrode surface, thetemperature of the cooling liquid can be below the boiling point of theliquid. If cooling liquid enters the furnace during operation, it wouldevaporate prior to reaching the molten metal bath and avoid explosion.The cooling liquid may also provide protection for various components ofthe cooling water system in fluid communication with the electrodecooling water. These components include, the spray nozzles, andcomponents on flow path 13 (e.g., control valves, flow meters, andpumps).

In most embodiments, the cooling liquid is constantly applied to theelectrodes. The application of cooling liquid can be generally held tobelow 4.5 m³/h for a 600-mm diameter electrode. Flow rates for smallerand larger electrodes can be varied based upon the surface coveragearea. Depending on the application, the flow rate may vary from 0.25m³/h to 10 m³/h, from 1 m³/h to 5 m³/h, or from 2 m³/h to 4 m³/h, foreach electrode (i.e., phase). The cooling liquid can be sprayed in adirection orthogonal to the longitudinal axis of the graphite electrode1, or at a downward or upward angle, e.g., of from 10° to 35° withrespect to the horizontal. The cooling liquid can be sprayed with a jetpressure of from 0.5 to 3 kg/cm² and at a rate of from 0.8 to 6.0l/minute, or up to 75 l/minute (about 20 gallons/minute), for eachelectrode. A sufficient amount of cooling liquid is sprayed at theelectrode to keep the electrode cooled. In this process, a sufficientamount of the cooling liquid is applied to the surface of the furnaceelectrode so that the protective coating is formed to reduce theoxidative electrode consumption, as compared to a like method in whichonly water cools the furnace electrode.

When the spray of cooling liquid 5 contacts the hot surface of thegraphite electrode 1, the cooling liquid evaporates to produce a coolingeffect on at least the portion of the electrode 1 above the furnace andto deposit the antioxidant additive, e.g., when the additive dissolvedsolids precipitates out of the cooling liquid. For example, as thecooling liquid flows down the exterior surface of the electrode, thewater evaporates, thereby concentrating the antioxidant additive in theremaining cooling liquid. When the concentration of the antioxidantadditive in the remaining cooling liquid reaches a saturation point, theexcess antioxidant additive will precipitate/deposit on the electrodesurface to form a protective barrier. The protective barrier made up ofthe antioxidant additive would also form when the remaining water in thecooling liquid is driven off.

In some embodiments, the electrode 1 can be cooled uniformly over itsentire length above the furnace. As the cooling liquid is sprayed ontothe portion of the electrode 1 above the furnace, this portion may becovered uniformly by the precipitates/deposits protective barrier. Asthe production of steel progresses, the electrode below the furnace canbe consumed by processes, such as tip sublimation, sidewall oxidation,and/or losses due to various forms of breakage, butt losses, andspalling. To account for these losses, the electrode can be moved orpushed into furnace so as to introduce portions of the electrode thatwas previously above the furnace into the furnace. Theprecipitates/deposits coating can then melt as it moves toward theinterior of the furnace to form a molten protective coating on at leasta portion of the electrode below the furnace.

FIG. 2 illustrates an example of the spray cooling arrangement for analternating current furnace. There are three electrodes in thealternating current furnace, and each of the electrodes supply one ofthe electrical phases.

Similar to FIG. 1, FIG. 2 includes a flow path 13 that allows thecooling liquid to flow to the spray cooling system. A control valve 9regulates the flow for spray cooling to an individual electrode, basedupon feedback 17 from a distributed control system (DCS) 7. An in-lineflow meter 10 measures the flow rate of cooling liquid and then sends afeedback 16 to the DCS 7 that actuates a pump 8 (e.g., a booster pump)to supply cooling liquid, which is pre-mixed offline. For example, theDCS 7 sends a feedback 14 to the pump 8 to supply the cooling liquid.The parameters (e.g., electrode and spray parameters) for this spraycooling arrangement can be the same or substantially the same as thosedescribed for FIG. 1.

FIG. 3 illustrates an example of the spray cooling arrangement for analternating current furnace. In this embodiment, the spray coolingarrangement includes a chemical metering skid 11 to supply theantioxidant additive in-line. The in-line flow meter 10 measures theflow rate of cooling liquid and then sends a feedback 16 to the DCS 7that actuates: (i) a pump 8 (e.g., a booster pump) to supply coolingwater, and (ii) a chemical metering skid 11 to supply the antioxidantadditive. For example, the DCS 7 can send a feedback 14 to the pump 8 tosupply the cooling water, as described above in connection with FIG. 2.The DCS 7 can also perform the calculations and send a digital or ananalogue feedback 15 to the chemical metering skid to supply theantioxidant additive at an accurate and discrete dosage. The dosage andthe timing between each dosage may be empirically determined. Forexample, the dosage and timing may depend on the furnace type, furnaceoperation, and the condition of the steel bath. The antioxidant additivecan be supplied from the chemical metering skid 11 in a neat form (ifliquid) or as a concentrated solution. The antioxidant additive can beintroduced to (e.g., injected into) the flow path 13 at location 12,downstream of the pump 8. Supplying the antioxidant additive at location12 can allow the mixing of the antioxidant additive with the water toform the cooling liquid. In some embodiments, the antioxidant additiveis introduced to the flow path 13 at a location upstream of the pump 8.The parameters (e.g., electrode and spray parameters) for this spraycooling arrangement can be the same or substantially the same as thosedescribed for FIGS. 1 and 2.

Accordingly, the consumption of the electrodes can be reduced throughthe application of an antioxidant additive in the electrode spraycooling liquid. The presence of the antioxidant additive in theelectrode spray cooling water allows for the formation of protectivebarrier at the same time the electrode is being cooled, and thus can bean efficient and effective method for reducing the oxidation of theelectrode.

Utilization of surfactants as an additive may enhance the performance ofthe cooling liquid and thus may further reduce the consumption rate ofelectrode. In some embodiments, the cooling liquid further comprises asurfactant or a blend of surfactants of the amount and type described inthe U.S. Provisional Application No. 62/745,729, titled “Spray CoolingFurnace Electrodes With A Cooling Liquid That Contains Surfactants,”filed on Oct. 15, 2018, the entirety of which is hereby incorporated byreference herein. The cooling water may include other additives such asbiocides, detergents, wetting agents, and the like.

Example 1

A cooling liquid containing water, sodium hexametaphosphate, andtetrasodium pyrophosphate was sprayed onto hot ultra-high-power (UHP)electrodes. Each electrode had a diameter of 400 mm. The cooling liquidcontained a total antioxidant additive amount of 500 mg/l. The sprayrate of the cooling liquid was dynamic and was based upon furnaceconditions in operation. The spray rate ranged between 3 gallons and 20gallons per minute per electrode during the heating of the electrode.Electrode consumption was reduced from about 2.3-2.5 lb/ton (seeComparative Example 1) to 1.8-2.0 lb/ton over a two-week evaluationperiod.

Example 2

This example tested the effect of a first and second additive on theoxidative consumption of an electrode at a steel manufacturing site.This site is a three phase EAF production facility, which experiences anaverage electrode consumption rate of about 2-3 lb/ton. The dosage ofthe first additive was first varied and then kept constant. When thedosage of the first additive was increased, increasing levels ofelectrode protection were confirmed, and the sidewall oxidation of theelectrode decreased. However, the maximum dosage of the first additivewas limited by the tendency of the cooling liquid to scale. (Similarobservations regarding the dosages and the levels of sidewall oxidationwere also observed in Examples 3 and 4 below.) Inspections of the sprayring and nozzles were regularly made to ensure proper water flow andspray pattern (to the electrodes) were obtained during the entirecampaign.

When the dosage of the first additive was held constant, the secondadditive was added to further study the impact on electrode consumptionrates. At the end of the trial period, a thorough study of the plantoperating data was conducted, and a reduction in electrode consumptionbetween 3% to 9% was observed. The specific reduction depended on thesteel melting practices that were used (i.e., operation conditions). Thereduction in electrode consumption over time is shown in FIG. 4. Thebold vertical line in FIG. 4 indicates the start of the trial period.

Example 3

This example tested the effect of a third additive composition on theoxidative consumption of an electrode at another steel manufacturingsite. This site is a three phase EAF production facility, whichexperiences high electrode costs and an average electrode consumptionrate of about 5-7 lb/ton. The study of the third additive was based onspray water chemistry and operational conditions of the plant. Variousdosages of the third additive were studied during the trial with finaldosage targets based on operational changes managed by the hostingplant. A constant dosage of the third additive was also studied. Thetest showed an electrode consumption reduction between 5% to 12% over a90-day test period, and further improvements are believed to bemanageable. The reduction in electrode consumption is shown in FIG. 5.The bold vertical line in FIG. 5 indicates the start of the trialperiod.

Example 4

This example tested the effect of a fourth additive composition on theoxidative consumption of an electrode at another North American steelmanufacturing site. This site is a three phase EAF production facility,which experiences initial high electrode costs and consumption rates.The study of the fourth additive was selected based on the plant spraywater chemistry and various operating constraints of the plant. Thedosage of the fourth additive was varied throughout a 90-day trial asdifferent operating conditions were evaluated. It was found that duringthe trial period the consumption of the electrodes were reduced, onaverage, by 6%.

Comparative Example 1

A cooling liquid containing water only was sprayed onto hotultra-high-power (UHP) electrodes. Each electrode had a diameter of 400mm. The spray rate of the cooling liquid was dynamic and was based uponfurnace conditions in operation. The spray rate ranged between 3 gallonsand 20 gallons per minute per electrode during the heating of theelectrode. The electrode consumption rate was determined to be 2.3-2.5lb/ton over a two-week evaluation period.

It will be apparent to those skilled in the art that variations of theprocess described herein are possible and are intended to be encompassedwithin the scope of the present invention.

1. A method for protecting a furnace electrode comprising: (i) mixing anantioxidant additive with electrode cooling water to form a chemicallymodified cooling liquid that includes at least 99 wt. % water, theantioxidant additive having a solubility in water of at least 1,000mg/L; (ii) while the furnace electrode is in service melting rawmaterials and a portion of the electrode is positioned inside a furnaceand another portion of the electrode is positioned above the furnace,spraying at least a surface of the furnace electrode that is positionedabove the furnace with the chemically modified cooling liquid at a flowrate of 0.25 m³/h to 10 m³/h, and (iii) while the electrode is beingsprayed with the chemically modified cooling liquid, forming aprotective barrier on the furnace electrode, the protective barriercomprising the antioxidant additive that is applied on the surface ofthe furnace electrode as the chemically modified cooling liquid flowsdown the electrode and water evaporates from the chemically modifiedcooling liquid, wherein the protective barrier is formed as a two-phasecoating that include (i) a first coating that comprises the antioxidantadditive which has been applied on the furnace electrode from thechemically modified cooling liquid, the first coating being located onan upper portion of an exterior surface of the electrode that is abovethe furnace; and (ii) a second coating comprising the antioxidantadditive in a molten state, the second coating being located on a lowerportion of the exterior surface of the electrode that is inside thefurnace.
 2. The method of claim 1, wherein the antioxidant additivecomprises a polyphosphate or a phosphate derivative.
 3. The method ofclaim 2, wherein the polyphosphate includes tetrasodium pyrophosphate.4. The method of claim 2, wherein the polyphosphate includes sodiumhexametaphosphate.
 5. The method of claim 1, wherein the antioxidantadditive comprises a calcium salt.
 6. The method of claim 5, wherein thecalcium salt includes calcium chloride.
 7. The method of claim 1,wherein the antioxidant additive is present in the chemically modifiedcooling liquid in an amount in the range of from 10 mg/l to 5,000 mg/l.8. The method of claim 7, wherein the antioxidant additive is present inthe chemically modified cooling liquid in an amount in the range of from50 mg/l to 1,000 mg/l.
 9. The method of claim 7, wherein the antioxidantadditive is present in the chemically modified cooling liquid in anamount in the range of from 100 mg/l to 850 mg/l.
 10. The method ofclaim 1, wherein the furnace electrode is an electric are furnaceelectrode or a ladle metallurgy furnace electrode.
 11. The method ofclaim 1, wherein a surface of the furnace electrode is at a temperatureof at least 700° C. while the furnace electrode is in service meltingthe raw materials and is being sprayed with the chemically modifiedcooling liquid.
 12. The method of claim 1, wherein a surface of thefurnace electrode is at a temperature of at least 1000° C. while thefurnace electrode is in service melting the raw materials and is beingsprayed with the chemically modified cooling liquid.
 13. The method ofclaim 1, wherein a surface of the furnace electrode is at a temperatureof at least 1200° C. while the furnace electrode is in service meltingthe raw materials and is being sprayed with the chemically modifiedcooling liquid.
 14. (canceled)
 15. The method of claim 1, wherein theantioxidant additive comprises (i) one or more component selected fromphosphates, phosphonates, calcium salts, magnesium salts, molybdates,boron salts, and silicates, and (ii) one or more component selected froma scale inhibitor and a dispersant. 16-20. (canceled)
 21. The method ofclaim 1, wherein the chemically modified cooling liquid is constantlysprayed on the surface of the furnace electrode disposed above thefurnace while the electrode is in service.
 22. The method of claim 1,wherein the chemically modified cooling liquid is sprayed on the surfaceof the furnace electrode disposed above the furnace at a flow rate inthe range of from 1 m³/h to 5 m³/h.
 23. The method of claim 1, wherein acontroller controls the flow rate of the chemically modified coolingliquid and the amount of antioxidant additive that is mixed with theelectrode cooling water.
 24. The method of claim 1, wherein theantioxidant additive includes a calcium based salt.
 25. The method ofclaim 1, wherein the antioxidant additive includes a surfactant. 26-27.(canceled)
 28. The method of claim 1, wherein the protective barrier hasa thickness in a range of from 0.005 to 0.3 mm. 29-30. (canceled)